WP6: Grid integration

Once the various options for the design and control strategy of the transnational grid have been investigated in Work Packages 1-3, and further optimized in WP5, the most promising results will be used as input for WP6. Large-scale steady-state and dynamic models will be developed to simulate the interaction between the transnational grid and the power systems of the neighbouring countries.

WP 6.1: Innovative grid planning and Operations concepts

Power exchange between the transnational offshore grid and the neighbouring onshore power systems is an important issue for two particular reasons. First, wind power should be transported to the onshore grid adequately by controlling the interconnector power flows. Second, remaining transport capacity should be efficiently used for international power exchange.

  • Planning: A long-term strategy will be determined that allows for the increase of wind power while the relative contribution of conventional generation is gradually decreased. A major challenge regarding this transition process is the constraint of having only a limited number of connection points for offshore wind, while conventional power plants were dispersed across the onshore network. Hence, a coordinated expansion plan will be devised that takes into account structural congestion issues that may arise in both the onshore and offshore networks.
  • Operations: How the transnational offshore grid can be operated in order to regulate power exchange correctly and avoid congestion will be investigated. Various power flow control strategies (e.g. centralized versus distributed control) will be investigated and a suitable control concept will be developed. Major influencing factors that should be taken into account are:
    • the prioritisation of wind with respect to conventional generation in case of congestion,
    • the accuracy of wind power forecasts in the time frame that international power exchanges must be scheduled (i.e. 36 hours in advance),
    • and finally the commitment and economic dispatch of conventional units in the onshore grids of the various partner countries.

WP 6.2: Impact of Transnational offshore grid on the stability of onshore networks

This research will focus on assessing the stability consequences of the transnational offshore grid on the AC grids of the adjacent countries, taking into account the gradual substitution of conventional generation by offshore wind.

  • Rotor angle stability will be investigated, with a focus on two main aspects.
    • Transient stability: The interconnected system must remain stable following major disturbances such as faults in the AC network. This type of stability is influenced by the amount of inertia from conventional units remaining in the system, and the fault-ridethrough behaviour of the offshore network.
    • Small-signal stability: At an interconnection point, large power fluctuations can occur due to wind gusts or remote network switching events. Nearby synchronously connected power plants can react to these fluctuations by oscillating against other generators in order to remain in synchronism with the power system. This research attempts to tackle the challenge of oscillation damping by using the VSC at the grid interconnection point. Since active power and voltage at a VSC interconnection point are fully controllable, the converter can act as a power system stabiliser by opposing the mentioned oscillations.
  • Voltage stability: depending on the amount of classical (CSC) HVDC connection points and installed AC cable lengths, voltage stability can become a problem. When results from previous work packages lead to the conclusion that it is indeed possible to operate the transnational offshore grid with a combination of CSC- and VSC-HVDC converters, onshore grid voltage stability must be thoroughly investigated.